The present invention relates to improving or reducing the black speck formation which frequently occurs during compounding and molding oxymethylene polymer molding compositions stabilized with polyamides having a melting or softening point below that of the oxymethylene polymer. More particularly, the present invention relates to oxymethylene polymer molding compositions containing a lower melting or softening polyamide stabilizer dispersed in a lower melting or softening carrier resin which composition may be molded into articles containing a reduced number of black specks.
Oxymethylene polymers, having recurring --CH.sub.2 O-- units have been known for many years. These polymers are used for a wide variety of molded articles. In the preparation of the molding compositions, minor amounts or portions of lower melting polyamides are frequently admixed with the oxymethylene polymer to improve the polymer stability during compounding and molding operations.
While the addition of the lower melting polyamides to oxymethylene polymers has provided excellent melt stability, black specks are commonly formed during both the compounding and the molding operations. As a result, the final molded article often contains black specks, thereby adversely affecting the appearance of the molded article. It is believed that the black specks are formed during both the compounding and the molding operations due to the reaction between free formaldehyde present in the oxymethylene polymer and the lower melting polyamide. The formaldehyde and polyamide are believed to react to form a gel-like substance which a dheres to the extrusion screws used in the compounding and the molding equipment. The gel becomes black with the passage of time at the compounding and molding temperatures; portions eventually break apart from the screws as black specks and end up in the compounded molding composition and eventually in the final molded object or article.
Accordingly, it is an object of the present invention to provide an oxymethylene polymer molding composition containing a lower melting or softening polyamide which has a reduced tendency to form black specks during compounding and molding operations.
These and other objects, as well as the scope, nature and utilization of the present invention, will be apparent to those skilled in the art from the following description and appended claims.